Semisynthesis of Dolabellane Diterpenes: Oxygenated Analogues with Increased Activity against Zika and Chikungunya Viruses.

Brown algae and soft corals represent the main marine sources of dolabellane diterpenes. The antiviral activity of dolabellanes has been studied for those isolated from algae, whereas dolabellanes isolated from soft corals have been barely studied. In this work, a collection of dolabellane diterpenes consisting of five natural and 21 semisynthetic derivatives was constructed, and their antiviral activities against Zika (ZIKV) and Chikungunya (CHIKV) viruses were tested. Dolabellatrienone (1) and (1R,7R,8R,11S)-7,8-epoxy-13-keto-dolabella-3,12(18)-diene (2), isolated from Eunicea genus soft corals, were employed to obtain 21 dolabellane and dolastane diterpenes by reactions such as allylic oxidations, reductions, acid-catalyzed epoxide ring opening, and acetylations. All of the compounds were identified by a combination of one- and two-dimensional NMR, mass spectrometry, and X-ray diffraction experiments. The cytotoxicites against Vero cells and the antiviral activities against ZIKV and CHIKV was tested to calculate the half-maximal effective concentration (EC50) and selectivity indexes (SIs). In general, the addition of oxygen-containing functional groups improved the bioactivity of dolabellane and dolastane diterpenes against ZIKV and CHIKV replication. Compound 9 showed an EC50 = 0.92 ± 0.08 µM and SI = 820 against ZIKV.

Dolabellane diterpenes from the Caribbean soft corals Eunicea laciniata and Eunicea asperula and determination of their anti HSV-1 activity / Dolabellanos de los octocorales caribenos Eunicea laciniata y Eunicea asperula y determinación de su actividad anti VHS-1 / Dolabellanos dos octocorais caribenhos Eunicea laciniata e Eunicea asperula e determinação de sua atividade anti HSV-1

Abstract Dolabellane diterpenes have considerable antiviral activity, but most studies have been focused towards compounds isolated from Dictyota brown algae. Although soft corals are also a significant source of these diterpenes, their antiviral potential has not been studied in detail. With the aim of assessing the biological activity of marine sources, we evaluated the dolabellane content in the soft corals Eunicea laciniata and E. asperula collected in Santa Marta, Colombian Caribbean. Dolabellanes 1-6 were isolated from E. laciniata while compounds 2, 4 and 5 were isolated from E. asperula. All compounds were identified by NMR, GC-EIMS, optical rotation and comparison with previously reported dolabellanes. GC-EIMS analyses showed that dolabellatrienone (2) transforms into compounds 4 and 5 as oxidation products upon prolonged storage; however, those compounds were also naturally present in the extract of the studied organisms. Pure dolabellanes were tested in vitro in antiviral assays against HSV-1. Compound 6 inhibited virus replication in infected cells (73.7% of inhibition at 50 µM) without cytotoxic effect (CC50 = 95 9), showing similar activity to the positive control Acyclovir®. Thus, compound 6 is an interesting candidate for further studies of dolabellanes as antivirals.

Resumen Los dolabellanos son diterpenos con actividad antiviral, la mayor parte de los estudios se han realizado con compuestos aislados de algas pardas del genero Dictyota. Los corales blandos son también una importante fuente de dolabellanos, pero el potencial antiviral de estos ha sido muy poco estudiado. Se llevó a cabo el estudio químico de los dolabellanos presentes en los octocorales Eunicea laciniata y Eunicea asperula, recolectados en Santa Marta, Caribe colombiano. Los dolabellanos 1-6 fueron aislados del octocoral E. laciniata mientras que en E. asperula se encontraron los compuestos 2, 4 y 5. La elucidaci6n estructural se llev6 a cabo mediante RMN, espectrometría de masas, rotaci6n 6ptica y comparaci6n con reportes previos. El análisis por CG-EM evidenci6 que la dolabellatrienona (2) se puede transformar en los compuestos 4 y 5 como producto del almacenamiento prolongado, no obstante, tales compuestos también estuvieron presentes en los extractos de los organismos estudiados. El compuesto 6 inhibi6 la replicaci6n del VHS-1 (73,7% de inhibición en células infectadas a una concentraci6n de 50 µM) sin efecto citot6xico (CC50 = 959), mostrando una citotoxicidad similar al Aciclovir®, un control positivo, por lo cual es un candidato para la realizaci6n de estudios adicionales sobre el potencial antiviral de los dolabellanos.

Resumo Os dolabellanos são diterpenos que têm mostrado atividade antiviral, os estudos neste campo estão centrados nos compostos isolados de algas do gênero Dictyota. Os octocorais também são uma fonte importante de dolabellanos, mas não tem sido estudados. Foirealizado o estudo químico dos octocorais Eunicea laciniata e Eunicea asperula, coletados em Santa Marta, Caribe Colombiano. O estudo químico dos dois organismos permitiu o isolamento dos dolabellanos 1-6 de E. laciniata, enquanto que para E. aspérula foram identificados os compostos 2, 4 e 5. A elucidação estrutural foi realizada mediante RMN, espectrometria de massas, rotação óptica e comparação com os dados da literatura. A análise por GC-MS evidenciou que a dolabelatrienona (2) pode gerar os compostos 4 e 5 como produto de degradação, a partir de um armazenamento prolongado. No entanto, os compostos também estavam presentes nos extratos dos organismos estudados. O composto 6 mostrou uma citotoxicidade similar ao Aciclovir®, um controle positivo, numa porcentagem de inibição da replicação do HVS-1 (73,7% de inibição em células infectadas na concentração de 50 µM) sem efeito citotóxico (CC50 = 959), o quetorna esse composto um candidato para o desenvolvimento de antivirais.

Marine Diterpenes: Molecular Modeling of Thrombin Inhibitors with Potential Biotechnological Application as an Antithrombotic.

Thrombosis related diseases are among the main causes of death and incapacity in the world. Despite the existence of antithrombotic agents available for therapy, they still present adverse effects like hemorrhagic risks which justify the search for new options. Recently, pachydictyol A, isopachydictyol A, and dichotomanol, three diterpenes isolated from Brazilian marine brown alga Dictyota menstrualis were identified as potent antithrombotic molecules through inhibition of thrombin, a key enzyme of coagulation cascade and a platelet agonist. Due to the biotechnological potential of these marine metabolites, in this work we evaluated their binding mode to thrombin in silico and identified structural features related to the activity in order to characterize their molecular mechanism. According to our theoretical studies including structure-activity relationship and molecular docking analysis, the highest dipole moment, polar surface area, and lowest electronic density of dichotomanol are probably involved in its higher inhibition percentage towards thrombin catalytic activity compared to pachydictyol A and isopachydictyol A. Interestingly, the molecular docking studies also revealed a good shape complementarity of pachydictyol A and isopachydictyol A and interactions with important residues and regions (e.g., H57, S195, W215, G216, and loop-60), which probably justify their thrombin inhibitor effects demonstrated in vitro. Finally, this study explored the structural features and binding mode of these three diterpenes in thrombin which reinforced their potential to be further explored and may help in the design of new antithrombotic agents.

4α-Acetoxyamijidictyol - A New Antifeeding Dolastane Diterpene from the Brazilian Brown Alga Canistrocarpus cervicornis.

Chemical investigation of the CH2 Cl2 crude extract from the brown alga Canistrocarpus cervicornis (Dictyotaceae) led to isolation of one new (1) and four previously reported dolastane diterpenes (2-5). Their structures were characterized by 1D- and 2D-NMR spectroscopic techniques, including a full single crystal X-ray diffraction analysis for 1, 2, and 4. In addition, the new structure 1 was assayed as chemical defense inhibiting the feeding by the sea urchin Lytechinus variegatus. This study constitutes an additional report broadening the known spectrum of action and defensive roles of secondary metabolites of the C. cervicornis and Dictyotales species.